https://en.wikipedia.org/wiki/Junkers_Jumo_004
Historically the Jumo 004 project was started just about the time that WW2 started in late 1939, even though the jet engine design war proven by Heinkel as a viable concept in 1937; supposing that the RLM took an interest in 1937 and set up several projects (Jumo and BMW) as competitors how much of a difference would it have made? As it was the Jumo project was pretty badly under resourced, having at its peak about 500 engineers, many of whom were taken straight from engineering school graduation for the program, rather than experienced engineers. IOTL the Jumo project was bench tested for the first time within about a year (October 1940, from a similar start date in 1939).

So would it not be reasonable that the first bench test happens then here some time in late 1938?

IOTL the first flight test was in March 1942, so that would be March 1940 here.

Assuming similar problems with the blade vibration and a similar time table to that solution (not guaranteed obviously, but I'm not sure what additional tech developments happened between 1940 and 1942 IOTL that would change things), the Jumo 004 could be ready for mass production in late 1942. The Me 262 wouldn't be ready until 1943, but with the engines working it would be ready to go in 1943 instead of late 1944.
Also with the additional two years ahead of OTL the Jumo developments with greater thrust and life span (the Jumo 004D was supposed to have had twice the life expectancy of the standard version), by 1944 the 004 would have been a more mature and useful engine.

Is this technically feasible or am I moving things forward too much? If it was possible and we go with the premise, what would the effect be on the air war of having jet engines relatively reliable and in mass production by June 1942? By 1943-44 they would have the production grove well set, so would be available in much larger numbers than IOTL and would use less fuel and less expensive fuel (diesel and kerosine mix IIRC), while being uninterceptable against Allied bombers in 1943 and probably 1944, especially if the LW can avoid the swarms of Allied fighters attacking their landing strips. The Mosquito would have a threat for once, even at night (the night fighter version was being successfully tested by the end of the war IOTL), while the Germans wouldn't have to spend money on useless bomber killer/night fighter projects like the Me 410 and He-219. It would also help save a lot of pilots that would have otherwise died at the hands of Allied fighters trying to get through to their bombers (no need for 1000 of the slow sturmböcke Fw190s with the Mk108, as the Me 262 would have not needed a fighter escort like they did and have heavier firepower and surviveability). Plus the major need then for the LW will be to have fighters to defend their Me262 coming back home and taking off, so the Fw190 would have been plenty good for airfield defense at lower altitudes, negating the advantage of the P51D when it appears in March 1944. Instead the Allies have to focus on killing the special aircraft, while the Axis fighters can focus on defending/escorting their jets at lower altitudes.

Keep in mind that the Me262 wasn't a dogfighter in the conventional sense, so it would have still been at a disadvantage in an escort rich environment. Perhaps if the He280 recieved the proposed engines it was designed for, then you would have a true fighter that would not only be capable of handling Allied fighters, but also fly top cover for the Me262 as it went to work as a bomber interceptor.

My understanding was that the Me262 was uninterceptable once the right tactics were worked out going after bombers; not only that, but it was seriously maneuverable at higher speeds and with the right tactics could take on enemy fighters pretty well if not sucked into a low speed turning battle.

Also as far as the He280 went, its engines never materialized despite Heinkel working on them since 1937, unlike the Jumo 004. But technically speaking was there any reason that the Jumo 004 couldn't have been available in 1942/43 if it had been started two years earlier? Could it have even been started that early?

I suspect it would have been a matter of getting the right people on the project –no simple matter with all the other immediate problems. One big advantage of an earlier effort would have been the availability of high temperature alloying metals from Sweden.

My understanding was that the Me262 was uninterceptable once the right tactics were worked out going after bombers;

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Which tactics? The problem was that when flying fast enough to make it impossible for the fighters to catch them the Me 262s had very little time to line up and fire at a bomber. In order to have a reasonable chance of hitting the bomber they slowed down, but then the escorts, particularly diving from above, could catch them.
I don't think that this classic "Catch 22" was ever really resolved.
The RAF carried out an interesting experiment with a Spitfire and an EE Lightning which illustrates the problem of a large closing speed in a much faster aircraft.
Cheers
Steve

A problem with some of these "early start" proposals is that often a lot was learned in the 2-5 years between the actual start of work and the "proposed" start of work. And in some cases even the historical start was done using rather inadequate test facilities let alone trying to use ( or not use) test facilities that might not have existed 2-3 years earlier.
For example there was a patent filed in July 1939 by Mueler and Junkers on the air cooling of turbine disks and blades. Even in 1940/41 work was being done on sections of the engines or scale models of the engine components to suit exiting test facilities and equipment. Again, as an example Junkers was working on a scaled down compressor such that it only absorbed 400hp to suit existing test equipment. The first Junkers jet engine, the RTO/RT 1 needed 4000hp to run it properly. The first engine/s never ran under their own power. They needed external power and a supply of compressed air to run at all. The first 12 stage axial compressor gave a total rise of 0.087 Ata at 6000rpm. Full speed was supposed to be 12,900rpm?
Some times a lot is learned even from failures.
The 004 was a simplified, austerity design. It took almost 3 years to go from initial proposal to flight test under a Bf 110. But some of the men who worked on it had worked on the earlier engine. Without the work done on the earlier engine haw much longer would it take?

A problem with some of these "early start" proposals is that often a lot was learned in the 2-5 years between the actual start of work and the "proposed" start of work. And in some cases even the historical start was done using rather inadequate test facilities let alone trying to use ( or not use) test facilities that might not have existed 2-3 years earlier.
For example there was a patent filed in July 1939 by Mueler and Junkers on the air cooling of turbine disks and blades. Even in 1940/41 work was being done on sections of the engines or scale models of the engine components to suit exiting test facilities and equipment. Again, as an example Junkers was working on a scaled down compressor such that it only absorbed 400hp to suit existing test equipment. The first Junkers jet engine, the RTO/RT 1 needed 4000hp to run it properly. The first engine/s never ran under their own power. They needed external power and a supply of compressed air to run at all. The first 12 stage axial compressor gave a total rise of 0.087 Ata at 6000rpm. Full speed was supposed to be 12,900rpm?
Some times a lot is learned even from failures.
The 004 was a simplified, austerity design. It took almost 3 years to go from initial proposal to flight test under a Bf 110. But some of the men who worked on it had worked on the earlier engine. Without the work done on the earlier engine haw much longer would it take?

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It can't be ready any later than it historically was, so maybe it only speeds things up for a year or 6 months, but that couldn't hurt Germany. It may not be a direct two years earlier is two years earlier to a completed engine, but even 6-18 months is an improvement, as nothing less will be learned in the meantime.

Which tactics? The problem was that when flying fast enough to make it impossible for the fighters to catch them the Me 262s had very little time to line up and fire at a bomber. In order to have a reasonable chance of hitting the bomber they slowed down, but then the escorts, particularly diving from above, could catch them.
I don't think that this classic "Catch 22" was ever really resolved.
The RAF carried out an interesting experiment with a Spitfire and an EE Lightning which illustrates the problem of a large closing speed in a much faster aircraft.
Cheers
Steve

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They would dive through a bomber box and pull up sharply to slow down briefly and shoot up the bombers from below before speeding off again as they leveled out or dove away again. This was completely uncounterable by escort fighters because the Me 262 was traveling way to fast for the whole process except for a couple of seconds, long enough to get off a burst with their Mk108s against the much larger target of B17s (the P51s are going to have a hard time acquiring the much smaller Me262 in the brief slowdown than the Me against the b17s).

The Me 262 was so fast that German pilots needed new tactics to attack American bombers. In the head-on attack, the closing speed, of about 320 m per second (350 yd), was too high for accurate shooting. Even from astern, the closing speed was too great to use the short-ranged 30 mm cannon to maximum effect. Therefore, a roller-coaster attack was devised. The 262s approached from astern and about 1,800 m higher (5,900 ft) than the bombers. From about 5 km behind (3.1 mi), they went into a shallow dive that took them through the escort fighters with little risk of interception. When they were about 1.5 km astern (0.93 mi) and 450 metres (1,480 ft) below the bombers, they pulled up sharply to reduce their excess speed. On levelling off, they were 1,000 m astern (1,100 yd) and overtaking the bombers at about 150 km/h (93 mph), well placed to attack them.[38]

Since the 30mm MK 108 cannon's short barrels and low muzzle velocity of 540 m/s (1,800 ft/s) rendered it inaccurate beyond 600 m (660 yd), coupled with the jet's velocity, which required breaking off at 200 m (220 yd) to avoid colliding with the target, Me 262 pilots normally commenced firing at 500 m (550 yd).[39] Allied bomber gunners found their electric gun turrets had problems tracking the jets. Target acquisition was difficult because the jets closed into firing range quickly and remained in firing position only briefly, using their standard attack profile, which proved more effective.[citation needed]

Captain Eric Brown, Chief Naval Test Pilot and C.O. Captured Enemy Aircraft Flight Royal Aircraft Establishment, who tested the Me 262 noted: "This was a Blitzkrieg aircraft. You whack in at your bomber. It was never meant to be a dogfighter, it was meant to be a destroyer of bombers... The great problem with it was it did not have dive brakes. For example, if you want to fight and destroy a B-17, you come in on a dive. The 30mm cannon were not so accurate beyond 600 meters. So you normally came in at 600 yards and would open fire on your B-17. And your closing speed was still high and since you had to break away at 200 meters to avoid a collision, you only had two seconds firing time. Now, in two seconds, you can’t sight. You can fire randomly and hope for the best. If you want to sight and fire, you need to double that time to four seconds. And with dive brakes, you could have done that."[39]

Eventually, German pilots developed new combat tactics to counter Allied bombers' defenses. Me 262s, equipped with R4M rockets, approached from the side of a bomber formation, where their silhouettes were widest, and while still out of range of the bombers' machine guns, fired a salvo of rockets with Hexogen-filled warheads. One or two of these rockets could down even the famously rugged B-17 Flying Fortress.[40]

Though this tactic was effective, it came too late to have a real effect on the war, and only small numbers of Me 262s were equipped with the rocket packs.[41] Most of those so equipped were Me 262A-1as, members of Jagdgeschwader 7.[42] This method of attacking bombers became the standard until the invention and mass deployment of guided missiles. Some nicknamed this tactic the Luftwaffe's Wolf Pack, as the fighters often made runs in groups of two or three, fired their rockets, then returned to base. On 1 September 1944, USAAF General Carl Spaatz expressed the fear that if greater numbers of German jets appeared, they could inflict losses heavy enough to force cancellation of the Allied bombing offensive by daylight.[citation needed]

The He280 was certainly capable of dogfighting and had the RLM showed interest in jet power early on, then the much needed funding for the projects would have definately seen an accelerated engine program (1939 - 1940). Even with the troublesom Hs engines the He280 operated at the time of it's trials allowed it to beat a Fw190 in a mock dogfight. This trial was done a few months before the Me262 prototype flew (1941).

The one attribute to the Me262's speed was that it could beat the P-51 in high-speed turns, but having to be careful not to bleed off too much speed where the P-51 would then become the hunter instead of the hunted.

So basically, if the RLM had shown an interest in jet technology when the He178 first flew in the late 30's and supplied funding for R D, then the jet program should have been able to work out alot of the bugs much earlier that were instead worked out during the chaos and material shortages of the middle-stages of the war.

It would have been very interesting to see how the He280 would have done with the intended Hs011

According to one book (author), the Initial work on the Jumo 004 was done with little regard to weight savings or the target thrust just to get something up and running. The A-0 version with solid high temperature blades was never intended to be the production version but again, was an interim version while the air cooled blades and other features were worked on. The shortage of elements needed for high temperature steel was no surprise and many of the same elements were also needed for other special steel alloys (like armor) and would be in short supply no matter what. In spite of an existing patent, it took time to work out the air cooled blades, which were a feature of the intended large scale production version from the beginning. The B-0 version was also an interim model with a number of changes from the A-0 but still with solid blades. Work on the air cooled blades had started in 1940 and was not a last minute "fix" or change.
With more effort (workers and money) and an earlier start, service introduction would have come sooner. But much of what was learned in 1936-40 still has to be learned instead of a design starting in late 1939/40 being able to use the 1936-39 knowledge right away.

They would dive through a bomber box and pull up sharply to slow down briefly and shoot up the bombers from below before speeding off again as they leveled out or dove away again. This was completely uncounterable by escort fighters because the Me 262 was traveling way to fast for the whole process except for a couple of seconds, long enough to get off a burst with their Mk108s against the much larger target of B17s (the P51s are going to have a hard time acquiring the much smaller Me262 in the brief slowdown than the Me against the b17s).

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I'll stick with the first hand experiences of both sides rather than a Wikipedia article. One thing an Me 262 definitely could not do was to go "speeding off" after slowing down for the attack. The Me 262 had very poor acceleration throughout its entire performance range. That was what lay at the heart of the "Catch 22".
Attacking with rockets whilst out of range of the bombers defensive fire was hardly a tactic developed for the Me 262. Even in the context of the article it is almost an admission that engaging with cannon at very high closing speeds was next to impossible. In fact very few Me 262s seem to have operated with the rockets.
Cheers
Steve

A good book to read regarding the Me262 and how it's pilots adapted to the new challenges the jets created, is "The Me262 Stormbird" by Colin Heaton Anne-Marie Lewis.

It covers a good deal of data and related first-hand accounts from the pilots themselves from the "schnell bomber" debaucle to the closing days of the war.

In there, the pilots recount how they attacked the B-17 with cannon and rockets, the best ways to fend off the escorts and the agaony of trying to land while the Allied fighters were lurking in the fringes, waiting to catch the Me262 at it's most vulnerable.

There were several instances where they closed on a B-17 and fired the Mk108 at nearly point blank range, only to have thier aircraft damaged as the B-17 was literally exploding in thier face from the catastrophic minengeschoss rounds.

It also covers in good detail the constant problems the Luftwaffe was having with the tempermental 004 as well as keeping the jets maintained and operable.

I'm under the impression Jumo 004 engine was derived from experience with earlier HeS 30 jet engine. This was cutting edge technology so unless you plan to go back in time with engine blueprints I don't see how it could begin earlier.

I think the futuristic axial compressor engine was too advanced and required too high a technology progress to be expected to be pushed forward significantly in operations. I think that had Germany pushed development of the centrifugal compressor engine, they could possibly have fielded a viable 2k lb thrust engine much earlier. The Brits could have also, had they been so enlightened to push the jet engine. I think the development risks of the centrifugal engine were much less than that of the axial version.

Historically the Jumo 004 project was started just about the time that WW2 started in late 1939, even though the jet engine design war proven by Heinkel as a viable concept in 1937; supposing that the RLM took an interest in 1937 and set up several projects (Jumo and BMW) as competitors how much of a difference would it have made?

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Simple answer, no. In 1937 the axial flow gas turbine was only a theoretical concept, and although it was investigated, it was thought of for driving propellers - turboprops and not as a pure jet. It was only in March 1937 that Ohain was carrying out bench testing on a hydrogen powered centrifugal flow He S 2 engine. You are presuming the two different engine types are based on the same technological principles and their development ran hand in hand, which they did not. The He S 3, again, a centrifugla flow engine, which powered the He 178 began flight testing in the summer of 1938 in an He 118.

Herbert Wagner, who is credited with the development of the first working axial flow gas turbine engine to power aircraft originally conceived it as a turboprop and patents were filed accordingly. The first working prototype was not completed and did not begin bench testing until 1939.

The axial flow compressor idea goes back to before WW I for naval and industrial use (shaft turbine). While more than a "theoretical" concept it wasn't of much use as the best of the experimental rigs could barely keep themselves running let alone actually provide power to do something (propel ship, run generator, run fans for steel mills, etc). The weight of such industrial engines was something on the order of 10lbs per hp, which while light compared to a steam boiler and turbine was way too heavy for aircraft which is why some some people scoffed at the idea of an aircraft turbine.
While in theory the axial flow turbine was better it took until the late 40s or early 50s for it to pass the centrifugal compressor. The Jumo 004 used an 8 stage compressor, each stage consists of a rotating disc with blades and a set of stationary blades between ( or after) each rotating disc. Get the blade shape or angle wrong and that "section" is either providing no compression or is 'stalling', it being quite possible for several stages to be doing all the work and other stages contributing nothing or actually being a obstruction. Using an axial flow compressor throws away everything they knew about the centrifugal compressors used as piston engine superchargers.
The Jumo 004 and BMW 003 both had about a 3:1 pressure ratio at a time when a good centrifugal compressor could reach 4:1, granted when work started on the axial flow jets a single stage centrifugal was nearer 3:1.

Germans also went for the axial flow because they thought they would need two engines to get the needed power and two under wing or in wing centrifugal engines would have too much drag. In this they were right, see Gloster Meteor with early engines. However in 1945-46 it was much easier to get modify (or scale up) the centrifugal engine to get much more power so later Meteor went much faster ( they had about double the power of early ones).

Perhaps what the Germans should have done (develop and use the jet earlier).
But not as a bomber destroyer, as a escort destroyer, or a air superiority fighter. Leave the bombers to the prop aircraft. The 110 could take out the bombers if Allied escorts could be stopped.
Of course if this happened, the Allies would accelerate their own jet fighter into service (Meteor). Maybe not as good as the 262, but in far greater numbers (US industry).
A different air war in Europe, but attrition would win for the Allies.

Germans also went for the axial flow because they thought they would need two engines to get the needed power and two under wing or in wing centrifugal engines would have too much drag. In this they were right, see Gloster Meteor with early engines. However in 1945-46 it was much easier to get modify (or scale up) the centrifugal engine to get much more power so later Meteor went much faster ( they had about double the power of early ones).

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They were aware of the concept of embedding the engine in the fuselage to reduce drag. The problem was two-fold, the first being the lack of apreciable thrust-to-weight and the other was they were simply out of time in regards to development.

A few examples:
Messerschmitt P.1101 which ironically, had a HeS 011A
Focke-Wulf Ta183 which was designed for the HeS 011 or Jumo 004

I think the futuristic axial compressor engine was too advanced and required too high a technology progress to be expected to be pushed forward significantly in operations. I think that had Germany pushed development of the centrifugal compressor engine, they could possibly have fielded a viable 2k lb thrust engine much earlier. The Brits could have also, had they been so enlightened to push the jet engine. I think the development risks of the centrifugal engine were much less than that of the axial version.

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Perfectly correct. It took years further development to get axial flow engines up to same levels of power, fuel economy and power as the centrifugal ones. Plus, whole new manufacturing technologies had to be developed, instead of being to springboard off of the existing supercharger manufacturing.

Basically it was a strategic mistake to go down that route, but a fortunate one for the Allies. The Germans had the excellent 262 airframe ready quite early one just waiting for the engines. If they had done a centrifugal design they could have had something very effective in the air in 43 quite easily.

I'm under the impression Jumo 004 engine was derived from experience with earlier HeS 30 jet engine. This was cutting edge technology so unless you plan to go back in time with engine blueprints I don't see how it could begin earlier.

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Other way around. Junkers engineers went to Heinkel-Hirth, where they developed the 109-006 (HeS 30) along side von Ohain's HeS 3.

The HeS 30 was cancelled in favour of the 109-011 (aka HeS 011), which incorporated axial and centrifugal (actually "diagonal") compressor stages.